Is it ensure, insure, or assure?
word-forming element meaning "around, about, enclosing," from Greek peri (prep.) "around, about, beyond," cognate with Sanskrit pari "around, about, through," Latin per, from PIE *per- (1) "forward, through" (see per).
Around; about; enclosing: perimysium.
A prefix that means: "around" (as in pericardium,) or "near" (as in perihelion).